Add python 3.13 tests, fixes:google-gemini#518

Change-Id: I9f46b79ad9a111cf47eb25fbab3553a4f2db005d

Author: MarkDaoust

.github/workflows/test_pr.yaml

@@ -15,6 +15,19 @@ on:
   workflow_dispatch:
 
 jobs:
+  test3_13:
+    name: Test Py3.13
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: actions/setup-python@v4
+      with:
+        python-version: '3.13'
+    - name: Run tests
+      run: |
+        python --version
+        pip install .[dev]
+        python -m unittest
   test3_12:
     name: Test Py3.12
     runs-on: ubuntu-latest